1. Field of the Invention
The present invention relates to a method of testing a light emission condition of an exposing head. The invention relates, more particularly, to a method for use with a type of exposing head which includes a plurality of luminous elements disposed along a main scanning direction for forming dots in the form of a dot-line on a print paper and which is movable in a sub scanning direction relative to the print paper, the method including the step of comparing light emission amounts of the luminous elements to each other based on the densities of the respective dots obtained by exposure of the print paper.
2. Description of the Related Art
As an example of the method described above, the following method is known. In this known method, by driving the luminous elements of the exposing head under a predetermined load condition over a print paper, there is formed, on the print paper, a testing dot pattern in the form of a dot-line, more particularly, as shown in FIG. 14a, a dot pattern Dp1 including a plurality of dots adjacently aligned along the main scanning direction of the exposing head. Then, by applying a scanner along this linear dot pattern thus formed on the print paper (actually, the developed image of the dot-line which is obtained by first forming the latent image of the dot pattern Dp1 on the print paper and then developing the image thereon), the densities of the respective dots are obtained, and the obtained density values, or any irregularities among them, are outputted as the testing result of the light emission condition of the exposing head
However, if the above test is conducted under such load condition as allowing the luminous elements to provide their full light emission performance, there occurs the tendency that in the dots formed on the print paper by the respective elements, one dot tends to extend into the adjacent area of another dot adjacent thereto. As a result, as shown in FIG. 14b which shows the principal portion of FIG. 14-a in an enlarged scale, there occurs overlapping between adjacent dots at their outermost portions. For this reason, in the step of determining the density of each individual dot by means of the scanner, the light emission condition of each luminous element cannot always be grasped with accuracy as each dot being influenced by its adjacent dot.
Then, as an improved method of testing a light emission condition of an exposing head devised to overcome the above problem, there is also known a method disclosed in the European patent published gazette EPO 925 941 (corresponding to the U.S. patent application Ser. No. 09/217,179) in the name of the same applicant as the present application. For overcoming the above problem, in this modified method, as shown in FIG. 15a and also in FIG. 15b which is an enlarged view, the method includes a first step of exposing and forming a plurality of arrays of dots (i.e. a plurality of xe2x80x9cdot-linesxe2x80x9d) on the print paper, each array including a plurality of dots equidistantly spaced from each other in the main scanning direction and also the dot arrays are spaced from each other in the sub scanning direction which is perpendicular to the main scanning direction and a second step of determining the densities of the respective dots of the resultant dot pattern Dp2 one array after another by means of a scanner.
According to the above method, the dots within each array are spaced from each other in the main scanning direction. Hence, there occurs no overlap between the dots, so that the density of each dot may be determined without influence from the adjacent dot. Further, as the dot arrays are also spaced from each other in the sub scanning direction, the scanning operation by the line scanner may be effected in a plurality of steps separately for the respective arrays. And, with these plurality of scanning operations combined, the densities of all dots may be obtained. Consequently, the intended object of accurate grasping of the light emission condition of the individual luminous element may be achieved with ease. Further, if the exposing head consists of blocks provided separately for the respective color components of R (red), G (green) and B (blue), by effecting the above-described process for each of these blocks, the light emission conditions of all of the elements used in the exposing head may be tested.
With the above method proposed by the co-pending patent applications identified above, the print page remains completely xe2x80x98blankxe2x80x99, after its exposure, at those inter-dot areas thereof between each pair of dots spaced apart from each other. Therefore, in the second step, namely, the step of determining the densities of the respective dots of each array by using a scanner, such blank areas will affect the measurement values, thus hindering accurate testing (more particularly, this seems to be attributable to a phenomenon that a portion of the irradiating beam emitted from the optical reflection type scanner employed in the second step is reflected by the blank area to be xe2x80x98flaredxe2x80x99 into the area of the dot which is the target dot of measurement, thus leading to inadvertent reduction in the measured density value.).
In view of the above-described drawbacks of the prior art described at the onset as well as the modified method of the invention described in the preceding patent applications, a primary object of the present invention is to provide a method of testing a light emission condition of an exposing head, which method is capable of overcoming such drawbacks of the prior art and achieving the original purpose of accurate grasping of the light emission condition of each luminous element of the exposing head.
For fulfiling the above-noted object, according to one aspect of the present invention, there is proposed a method of testing a light emission condition of an exposing head, which comprises the following:
(1) a first step of forming latent images of testing target dots on a print paper by driving luminous elements selected as target elements which are not adjacent each other in the main scanning direction;
(2) a second step of forming latent images of background dots in the peripheries of the latent images of the target dots so that the peripheries are completely filled with the latent images of the background dots with a density above a predetermined value;
(3) a third step of developing the latent images of the target dots and the background dots formed on the print paper and subsequently determining the densities of the respective developed images of the target dots by using a scanner; and
(4) a fourth step of outputting the density of each one of the target dots obtained by the third step as a light emission amount of each corresponding luminous element selected as one of the target elements.
According to the invention""s method of testing a light emission condition of an exposing head having the above construction, in the first step, there are obtained latent images of target dots which are not adjacent each other in the main scanning direction; and in the third step there are determined the densities of the developed images of these target dots without mutual overlaps therebetween. Hence, the density of the individual dot may be determined with accuracy, without influence from the adjacent dots. Moreover, in the density determination of the third step, this determination is made with the periphery of each target dot being filled with the images of the background dots without leaving any blanks therein. Therefore, this method is free from the disturbance due to the xe2x80x98flaringxe2x80x99 of the irradiating beam emitted from the optical reflecting scanner. Consequently, the light emission condition of each luminous element may be readily grasped with accuracy.
Preferably, the first step includes following sub steps:
(1-1) a first sub step of forming a latent image of a first dot array by driving at one time those luminous elements of the exposing head assigned for odd-numbered pixels; and
(1-2) a second sub step of forming a latent image of a second dot array by driving at one time further luminous elements of the exposing head assigned for even-numbered pixels at a position spaced from the latent image of the first dot array in the sub scanning direction.
With this construction, the dots by all of the luminous elements required for formation of a linear testing dot pattern may be formed with just two times of exposure operation. As a result, the method of a light emission condition of an exposing head may be carried out more efficiently.
Preferably, the density of the background dot is set to be 50 to 60% of that of the target dot. With this setting, the flaring interference by the scanner beam with the density determination may be restricted sufficiently. This construction provides the further advantage of restricting such reverse effect as the background dots formed for the purpose of eliminating blanks in the peripheries of the target dots might actually increase the density of the area of the target dot, thus hampering accurate density determination thereof.
According to a further aspect of the present invention, there is proposed a testing dot pattern to be obtained by exposure on the print paper for comparing the light emission amounts of the respective luminous elements of the exposing head described in claim 1, which testing dot pattern comprises: target dots formed on the punt paper by driving luminous elements selected as target elements which are not adjacent each other in the main scanning direction; and background dots formed in the peripheries of the respective target dots, the background dots having a density above a predetermined value.
Preferably, the relative light emission amounts of the respective luminous elements are obtained by determining the densities of the target dots by using a scanner; and the testing dot pattern further includes position-index dots for providing position information of the target dots to the scanner.
With the above construction, the print paper bearing the image of the testing dot pattern developed by a developing operation will be set on e.g. a flatbed scanner to be scanned thereby. With this one-step operation alone, the line scanner incorporated in the flatbed scanner may calculate the position of each target dot within the testing dot pattern based on the corresponding position information and may determine its density automatically.
More specifically, the position-index dots may include main-scanning index dots relating to position information respecting the main scanning direction and sub-scanning index dots relating to position information respecting the sub scanning direction; and the main-scanning index dots may include odd-pixel main-scanning index dots formed by luminous elements for odd-numbered pixels and even-pixel main scanning index dots formed by other luminous elements for even-numbered pixels.
Further and other objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments thereof with reference to the accompanying drawings.